Context. It is plausible that at least part of the water ice of cometary
nuclei is initially in an amorphous phase, doped with other
volatiles. As the nuclei are heated, the amorphous ice would then transform
irreversibly into cubic ice. The net energy liberated in this
transformation may be affected by the presence of any impurities because
part of the energy liberated during crystallization may be expended
in the desorption of dopant elements.

Aims. Our goal is to study the evolution of the crystallization front of the amorphous ice in a simulated nucleus, providing quantitative results. In particular, the influence of the net energy released during crystallization on the
thermophysical evolution will be analyzed.

Methods. We use a simplified thermophysical model to simulate a cometary nucleus, where the ice
is assumed initially to be in an amorphous phase. The model allows
us to estimate the instantaneous rate of crystallization and the time spent in crystallization, for a fixed
volume of amorphous ice, as a function of the net energy
released. Simulations are performed for different
characterizations of the nucleus interior such as dust-to-ice ratio, density, or thermal inertia.

Results. As expected, the evolution of the crystallization front depends strongly on the characteristics of the nucleus interior.
If the nucleus interior has, however, a dust-to-ice ratio smaller than 1,
and a low thermal inertia, approximately of 20 W K-1 m-2 s1/2,
the crystallization front evolves discontinuously, with quasi-periodic
increases in the crystallization rate. Those increases have a
period that ranges from 1 to 40 days, if the energy released by crystallization is unaffected by impurities. These surges of crystallization could be responsible for the periodic outbursts observed for comet 9P/Tempel 1 shortly before the Deep Impact experiment.
The evolution of the crystallization front
becomes continuous and almost steady, if the net energy released is half that of the pure, exothermic case, regardless of the
characteristics of the nucleus interior.
On the other hand, if the dust-to-ice ratio is high (larger than 1) and/or the thermal inertia is high (larger than 100), the crystallization front evolves in a continuous and smooth manner, even for pure, exothermic crystallization. Other quantitative
results, including a comparison with plausible erosion rates, are described.

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.